Artificial leathers are commonly produced by a method wherein an elastic polymer is applied on a nonwoven fabric obtained by intertwining ultrafine fiber-generating fibers, and the ultrafine fibers are generated to thereby produce the artificial leather. The methods commonly used in the intertwining of the ultrafine fiber-generating fibers include needle punching and water jet punching, and the intertwining by the needle punching is known to generally involve complicated events due to the friction between the needle material and the fiber as well as rigidity, strength, and crimping of the staple fiber.
Artificial leathers are likely to have higher quality and superior physical properties such as abrasion properties when the sheet such as the nonwoven fabric constituting the base body for the artificial leather has a higher fiber density and highly dense texture. Accordingly, it has been a general requirement that the base body for an artificial leather is a sheet having a high degree of intertwining and density.
One solution to such requirement is increase in the number of punching in the needle punching to facilitate the fiber orientation in thickness direction. In view of such situation, use of a polymer capable of forming a fiber with higher rigidity had been preferred so that the fiber can endure repeated needle punching. For example, a particular type of highly rigid polystyrene has been used for the sea component of the islands-in-the-sea conjugated fiber which is a fiber known for use in generating the ultrafine fiber for the purpose of realizing high degree of intertwining in the needle punching (see Patent Document 1). However, the number of needle punching that could be effected in this method has been limited due to the amorphous and brittle nature of the polystyrene, and a base body for an artificial leather having a fully sufficient degree of density and intertwining is not yet realized.
In view of such situation as well as recent rise of environmental consciousness, production of an artificial leather by a process not using an organic solvent has gained attention, and various investigation have been made with the attempts of using a crystalline copolymerized polyester which is readily soluble by an alkali treatment for the sea component in the generation of the ultrafine fiber (see Patent Document 2).